This invention relates in general to improvements in internal combustion engines and, more specifically, to a system for directly injecting fuel into an engine cylinder through the cylinder sidewall.
Over the years, a great deal of research and development effort has been expended toward achieving improved fuel efficiency together with reduced exhaust emissions in internal combustion engines. Higher compression ratios are usually beneficial in these areas. However, detonation rapidly becomes a problem unless high octane fuels or octane enhancing additives are used. High octane fuels are costly, and the enhancing additives often contribute to exhaust emission problems.
Many engine design and operational improvements have been made to allow higher efficiency with lower octane fuels. These include improvements in ignition control, in particular with computer controlled spark advance systems, improvements in valve timing, improved fuel delivery systems, in particular fuel injection systems, and combustion chamber design enhancements.
Significant advancements have been made in combustion chamber design, such as are described in my copending U.S. patent application, Ser. No. 07/995,785, filed Dec. 23, 1993.
Improvements in fuel delivery to these combustion chamber designs, or others, would further improve engine efficiency. Fuel injection systems in which fuel is indirectly injected as a spray either into a throttle body and ducted to the combustion chambers or into intake ports feeding combustion chambers are rapidly replacing carbureted systems. Under computer control, much more precise metering of fuel, improved fuel distribution and improved air delivery capacity, etc. are possible with fuel injection.
Single point injection systems where the fuel is injected into either the induction manifold of the throttle body suffer many of the problems generally associated with carburation. These include unequal mixture distribution to different cylinders and deposition of fuel on manifold walls. Multi-point port fuel injection provides a more even fuel distribution but raw fuel is still a problem on port walls and intake valves.
With direct fuel injection into the combustion chamber, the injector is ordinarily installed in the cylinder head, often at the top center of the combustion chamber to provide optimum fuel spray with minimal wall wetting. To avoid waste of fuel, valve arrangements must be designed to prevent fuel loss through the exhaust port during scavenging. Port or throttle body ;injection can utilize up to 720.degree. of crankshaft rotation in a four-stroke engine. However, this sprays raw fuel onto the back of a closed intake valve resulting in liquid fuel on the port walls and valve and allows raw fuel to pass out of the exhaust port at overlap. This can also result in bore wall wetting, fouled spark plugs, worn piston rings, incomplete combustion, misfire, etc.
Direct injection into the combustion chamber directly from the cylinder head during the intake stroke has advantages over throttle body injection. However, these injectors tend to be high in cost due the necessity of resisting high chamber pressures and temperatures and often causes bore wall wetting resulting in excess piston ring wear, crankcase contamination and elevated hydrocarbon emissions.
A number of different arrangements for injecting fuel directly or indirectly into combustion chambers have been developed. Fuel may be injected into the side of the combustion chamber tangentially to cause a rich mixture to swirl past the spark plug. While effective in industrial power units running mainly at constant speed, difficulties in controlling swirl and stratification throughout the range and speeds of automobile engines and the like has limited the usefulness of this design. Other designs used a bowl-in-piston combustion chamber and an axial injector with either early or late injection, relative to the time the piston approaches top dead center. Maintaining an optimized stratified charge over a wide range of power loading has proven difficult.
Direct injection systems often have problems with depositions of fuel droplets on the cylinder walls followed by variable and incomplete evaporation, poor mixing of fuel and air that results in fuel/air separation problems. These produce cylinder to cylinder mixture uniformity problems.
There is a continuing need for improvements in the fuel injection system and its relationship to the combustion chamber to provide better atomization, lower exhaust emissions and an improved tolerance for lower octane fuel.